When standard error diffusion is applied to scanned documents in the copy image path, many isolated dots are created in the resultant image. Some print engines are not capable of printing/reproducing these isolated pixels accurately and systematically, which leads to unwanted image quality artifacts in the copies, such as uneven and patchy image areas. The image quality of text and line art is also impacted, even in the case of high addressable printing.
Rank order error diffusion (ROED), such as disclosed by (i) R. Loce et al., in U.S. application Ser. No. 09/968,651, filed Oct. 1, 2001, (U.S. Publication 20030090729) for, “RANK-ORDER ERROR DIFFUSION IMAGE PROCESSING”; (ii) R. Loce et al., in U.S. application Ser. No. 11/034,057, filed Jan. 13, 2005, for “SYSTEMS AND METHODS FOR CONTROLLING A TONE REPRODUCTION CURVE USING ERROR DIFFUSION”; (iii) B. Xu et al., U.S. application Ser. No. 11/013,787, filed Dec. 17, 2004 for “SYSTEMS AND METHODS FOR RANK-ORDER ERROR DIFFUSION IMAGE PROCESSING”; and (iv) Y. Zhang et al., U.S. application Ser. No. 10/923,116, filed Aug. 20, 2004, for “UNIFORMITY COMPENSATION IN HALFTONED IMAGES”, all of which are hereby incorporated in their entirety for their teachings, has numerous applications and is an excellent starting step for eliminating artifacts in non high addressable output. However, some artifacts are likely to remain. In the high addressable binary image context, rank order error diffusion combined with compact high addressable pixel creation, as described for example in (i) U.S. application Ser. No. 11/034,057; (ii) U.S. application Ser. No. 11/013,787; and (iii) U.S. Pat. No. 6,683,702 to R. Loce et al., for “Compact-Dot Reproduction of Scanned Halftone Screens,” also incorporated by reference in its entirety, generates unwanted patterning artifacts.
Implementation of rank order error diffusion as described in (i) U.S. application Ser. No. 09/968,651; or (ii) U.S. application Ser. No. 11/104,758, by R. Loce et al., filed Apr. 13, 2005, for “BLENDED ERROR DIFFUSION AND ADAPTIVE QUANTIZATION”, also hereby incorporated by reference in its entirety, may be prohibitive in high-speed image paths. Rank order error diffusion is also disclosed in: U.S. application Ser. No. 11/218,966, by R. Loce et al., filed Sep. 2, 2005 for “COLOR MANAGEMENT OF HALFTONED IMAGES”, which is also hereby incorporated by reference in its entirety.
Accordingly, a modified and less computationally intensive ordered error diffusion method, a different technique of generating the high addressable binary output, and a different technique of calculating the quantization error based on local context, are needed for the copy path to meet increased throughput speed and image quality requirements. The disclosed system and method provide a binary image generation method using ordered error diffusion with optimized and improved image processing speed and image quality for eliminating printing artifacts for digital output such as copies.
Disclosed in embodiments herein is a method for processing an input image, comprising: creating binary output by thresholding a current grayscale input image pixel and an associated intermediate predicted pixel value; calculating a pixel quantization error based upon the current image pixel value and the intermediate predicted pixel value; ordering a plurality of neighboring pixels of the current pixel located in a predefined processing window according to their gray values; diffusing a maximum possible amount of quantization error for the current image pixel sequentially to a subset of the plurality of neighboring pixels of the current pixel, where the subset of the plurality of neighbors are selected in accordance with the sign of quantization error; and repeating the steps above for each input pixel in the image to produce an error-diffused output image.
Also disclosed in embodiments herein is a method creating a halftoned image, comprising: receiving a pixel value from an input image; selecting an processing window encompassing M neighboring pixels; selecting a threshold; thresholding the pixel value with the selected threshold to make a binary marking decision; calculating a quantization error value based on the pixel value and the binary marking decision; and diffusing quantization error to at least one selected neighboring pixel(s) N within the diffusion mask M, based on the calculated error value, the selection being based on pixel values of a plurality of neighboring pixels within the diffusion window.
Further disclosed in embodiments herein is a digital reprographic system, comprising: an image source; an image processor, for processing each input pixel of an input image from said image source to produce an error-diffused output image, said image processor including a thresholder for creating binary output and an associated intermediate predicted pixel value as a function of a current image pixel; a pixel error calculator for calculating pixel quantization error based upon the current image pixel value and the intermediate predicted pixel value; a pixel ordering circuit for ordering the current input image pixel's M neighboring pixels located in a predefined processing window according to their gray values, said ordering circuit further diffusing the quantization error for the current image pixel sequentially to N out of the M neighbors of the current pixel, where N is not greater than M; where the N neighbors are selected depending on the sign of quantization error, and an image output terminal for outputting the error-diffused output image.